From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jamie Lokier Subject: Re: [patch 0/2] Run interrupt handlers always with interrupts disabled Date: Fri, 26 Mar 2010 12:02:28 +0000 Message-ID: <20100326120228.GC19308@shareable.org> References: <20100326000325.917127328@linutronix.de> <20100326081457.GA23570@flint.arm.linux.org.uk> <20100326092023.GH27394@elte.hu> <1269595692.12097.128.camel@laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail2.shareable.org ([80.68.89.115]:36531 "EHLO mail2.shareable.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752672Ab0CZMCs (ORCPT ); Fri, 26 Mar 2010 08:02:48 -0400 Content-Disposition: inline In-Reply-To: <1269595692.12097.128.camel@laptop> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Peter Zijlstra Cc: Ingo Molnar , Thomas Gleixner , Nicolas Pitre , Linus Torvalds , LKML , linux-arch@vger.kernel.org, Andrew Morton , Alan Cox , Andi Kleen , David Miller , Greg Kroah-Hartman , Arnaldo Carvalho de Melo , Russell King Peter Zijlstra wrote: > On Fri, 2010-03-26 at 10:20 +0100, Ingo Molnar wrote: > > * Russell King wrote: > > > > > On Fri, Mar 26, 2010 at 12:06:44AM -0000, Thomas Gleixner wrote: > > > > The following patch series removes the IRQF_DISABLED functionality > > > > from the core interrupt code and runs all interrupt handlers with > > > > interrupts disabled. > > > > > > As was covered in previous discussions, what about drivers such as SMC91x > > > which take a long time to retrieve packets from the hardware? Always running > > > handlers with IRQs disabled will kill things such as serial on these > > > platforms. > > > > As long as it's rare (which it is) i dont see a problem: you can enable > > interrupts in the handler by using local_irq_enable(), like the IDE PIO > > drivers do. That way it's documented a bit better as well, because it shows > > the precise source of the latency, with a big comment explaining it, etc. > > Or alternatively, use threaded interrupts for such slow hardware. What is the latency of threaded interrupts these days, compared with non-threaded interrupts? Slow hardware is quite sensitive to increases in latency. Obviously not a problem for the sources of latency: it's a problem for the irq which is _sensitive_ to latency caused by the other one. That is typically a serial port or something. But the benefit of kernel-settable interrupt priorities (i.e. due to the threads) may be worth it even for serial ports. I would love to see some measurements comparing with and without. -- Jamie